Introduction:
Sensors are the eyes and ears of every automation system. From detecting bottle positions on conveyors to monitoring tank levels and temperatures, sensors are crucial for accuracy, efficiency, and safety in industrial processes.
In this post, we’ll cover the major types of industrial sensors, where they are used, and how to choose the right one for your application.
1. Why Are Sensors Important in Automation?
In any PLC-controlled system, sensors feed real-time data that drives decisions:
- When to start/stop motors
- Detect object presence
- Measure process variables (e.g., temperature, pressure)
- Ensure system safety
Without sensors, automation would operate blindly — and dangerously.
2. Common Types of Industrial Sensors
a) Proximity Sensors
- Inductive Sensors – Detect metal objects without contact
Use for: Sensing machine parts, metal targets - Capacitive Sensors – Detect metal & non-metal objects like plastic or wood
Use for: Presence detection on packaging lines
b) Photoelectric Sensors
- Use light beams to detect object presence
Types: Through-beam, retro-reflective, diffuse
Use for: High-speed object detection on conveyors
c) Ultrasonic Sensors
- Use sound waves to measure distance
Use for: Level detection in tanks, object spacing
d) Temperature Sensors
- RTD (Resistance Temperature Detector) – Accurate and stable
- Thermocouple – Handles high temperatures
Use for: Boiler control, ovens, chillers
e) Pressure Sensors
- Convert pressure into electrical signals
Use for: Monitoring compressors, hydraulic lines, pumps
f) Flow Sensors
- Measure flow rate of liquids/gases
Use for: Water treatment plants, bottling lines
g) Level Sensors
- Detect level of solids/liquids in tanks
Use for: Silos, chemical dosing, beverage mixing
3. Analog vs Digital Sensors
- Digital Sensors: Simple ON/OFF signals (e.g., object detected or not)
- Analog Sensors: Send variable signals (e.g., 4–20 mA, 0–10 V) based on physical quantity measured
Use analog for: Precision control in temperature, flow, or pressure
4. Sensor Selection Tips
- Understand the application – What are you measuring? Solid, liquid, gas?
- Check environmental conditions – Temperature, humidity, dust, IP rating
- Determine sensing range and accuracy
- Evaluate connection type – PNP vs NPN for digital, or signal range for analog
- Ensure compatibility with your PLC
5. Troubleshooting Common Sensor Issues
- Sensor not detecting: Check alignment, dirt, power supply
- Fluctuating signals: Use filters or shielded cables
- Analog signal drift: Calibrate sensor regularly
- Interference: Avoid running signal cables near power cables
Conclusion
Sensors are the foundation of smart automation. Choosing the right sensor type — and understanding how it behaves — is essential to building stable, accurate, and intelligent systems.
Whether you’re an automation newbie or building a new line, mastering sensors is your first step toward expert-level control.
Next Steps:
👉 Bookmark this guide
👉 Subscribe on PLCExpertHub.com for a downloadable sensor cheat sheet
👉 Share with your team — especially new techs!